Electrical amplifier circuits



March 6, 1934. A HUND 1,950,003

ELECTRICAL AMPLIFIER CIRCUITS Filed Dec. 9, 1931 v 2 Sheets-Sheet 1 POWER r52 INVENTOR Auqust Huml 'yW/m ATTORNEY March 6, 1934. HUND 1,950,603

ELECTRICAL AMPLIFIER CIRCUITS Filed Dec. 9, 1931 2 Sheets-Sheet 2 49 POWER INVENTOR A l lgust Hunfl ATTORNEY Patented Mar. 6, 1934 UNITED STATES FATE,

FFECE ELECTRICAL AMPLIFIER CIRCUITS tion of Delaware Application December 9, 1931, Serial No. 579,872

4 Claims.

This invention relates to electrical amplifying systems and particularly to circuits for such systems in which discharge tubes are employed.

Electrical amplifiers of types such as thermionic 5 tubes are well known, these tubes having h ated cathodes emitting electrons the passage of which to positive electrodes being controlled by third electrodes. These amplifiers have certain disadvantages, however, when amplifying currents over a broad band of frequencies, and in the amplification of power where the utilizing device or load has a low input impedance. It is also well known that considerable energy must be supplied to this type of amplifier to heat the cathode and polarize the control and anode electrodes.

The present invention contemplates an ampliher which is substantially free from these disadvantages and which can be so constructed as to faithfully amplify currents of frequencies not possible with known types of amplifiers, the amplification factor being high both with respect to voltage and power. The hereinafter described discharge tube requires no energy consuming electrode such as a hot filament and does not require a control electrode voltage although the latter may be used in certain instances which will be described hereinafter.

An object of the invention is to amplify electrical vibrations in the form of voltage, current or power.

' Another object of the invention is to amplify electrical energy with the use of a discharge tube having only cold electrodes.

A further object of the invention is to amplify high frequency electrical currents over a broad band of frequencies in a high frequency range.

A still further object of the invention is to efficiently amplify electrical voltages and energy at an extremely high ratio.

The invention in brief, comprises an electrical discharge tube having at least three cold electrodes with input and output circuits, and a polarizing source for polarizing two electrodes while the third is disposed and employed as a control electrode.

It has been found in the development of this amplifying tube that at certain polarizing voltages and with the proper circuit constants forming the input and output circuits of the tube, power amplification factors of 50, or more, are possible, While a voltage amplification of or more fold has been obtained. Such a tube may be made to have a low output impedance compared with the present day thermionic vacuum tubes having heated cathodes which makes it especially adaptable for power amplification for reproduction purposes. Another important feature that has been found by experimentation is that the input impedance of the tube may be made to increase with frequency, an especially desirable feature when plural stages of amplification of carrier and the higher frequency currents are required. These features have been found to exist over a considerable range of frequencies while it is possible to control the frequency band of amplification by the construction of the tube, the gaseous content, and pressure.

The invention will be more fully understood by reference to the following description, read in conjunction with the accompanying drawings in which:

Fig. l is a schematic circuit of a single stage amplifier employing a three cold electrode tube;

Fig. 2 is a schematic circuit of a single stage amplifier showing adjustable circuit connections therefor;

Figs. 3 and 4 show plural stage amplifiers energized from a single power source the circuit of Fig. 3 having resistance coupling and that of Fig. i, transformer coupling, and

Fig. 5 shows a plural stage amplifier circuit with a modified form of power supply.

Referring specifically to Fig. 1, a three cold electrode discharge tube 5 has a cathode 6, anode '7, and a control electrode 8. This tube is evacu- 8 ated to a pressure in the neighbourhood of 15mm. but this pressure will vary in accordance with the characteristics desired from the tube. Any suitable gas may be used such as air, helium, neon, argon, or the like, although the results 9 0 desired determine which gas is preferable. All the electrodes may be of various shapes and sizes, special attention being paid to the positioning of the electrodes in a manner to provide the greatest control eifect upon the glow therein. By po- 95. sitioning the control electrode at a place where there is either an excess of negative ions which are preferably electrons, or an excess of positive ions, excellent control is obtainable. Another action which has been found to provide an amplification is that certain tubes exhibit negative resistance characteristics, as disclosed in my copending application Serial No. 573,076 filed Nov.

5, 1931, while in certain other constructions, the control electrode controls the relaxation current in the output circuit or main branch, but only during the time the input voltage exists.

It is to be understood of course, that the construction and positioning of these electrodes control the operating characteristics of the tubes to a substantial degree. Details of the construction of these tubes are disclosed and claimed in my copending application Serial Number 603,284 filed April 5, 1932.

The cathode 6 and control electrode 8 are connected to the input circuit which comprises the secondary of an input transformer 10, a glow fixing battery 11 and rheostat 12. The anode '7 has a positive potential supplied thereto from a source 14, through the adjustable output and protective resistance 15, the output circuit being taken off across this resistance through blocking condensers l6 and 1'7. Two bypass condensers 18 and 19 are employed in this circuit, the former being across the biasing battery 11 and rheostat 12, and the latter across the anode potential source 14. This circuit is especially flexible and will amplify electrical voltages in high frequency ranges with a comparatively constant and high gain, although the system is applicable to currents of any frequency. A feature of this circuit is the use of battery 11 which permits the fixing of the glow at the most efiicient part of the tube. This battery may be eliminated entirely by making source 14 adjustable, and by using a resistance condenser combination 9, 13, as in Fig. 2, but it is advantageous when the source 14 is fixed and not subject to easy adjustment. With the battery 11 omitted and the external resistance low, the tube amplifies in effect as a two electrode device through its negative resistance action, as mentioned above.

Referring now to Fig. 2 a similar discharge tube 5 is shown with corresponding electrodes 6, 7 and 8. In this particular circuit, the input return from the control electrode 8 may be transferred from the cathode 6 to the anode '7 by means of a switch 20, it having been found that either the anode or cathode return is operative, and with certain tube constructions, one may be preferable. In this circuit, as in Fig. 1 the anode potential is supplied from the battery 14 shunted by bypass condenser 19 in series with the output protective resistance 15. Any direct voltage source may be employed of course. The output circuit is shown including an output transformer 22 connected across the output resistance through the blocking condenser 16. Another feature of this circuit is the tuning of the input circuit, which is accomplished by a tuning condenser 23 across the secondary of the input transformer 10. By tuning the input of the tube, selectivity is obtained. A variable resistance 9 shunted by a condenser 13 so as not to decrease the input voltage is shown in the input circuit of the tube, the resistance causing the proper potential difference to exist between the electrodes '7 and 8.

In Fig. 3 a two stage amplifier has two tubes 25 and 26 similar to those shown in Figs. 1 and 2 connected in tandem. The input circuit of tube 5 includes an input transformer 27, and the output circuit of tube 26 includes an output resistance 28, and blocking condensers 29 and 30. The power source 32, which may be either a direct current source or a rectifier supplied from alternating current, supplies voltage to a potentiometer having two portions 33 and 34 with appropriate bypass condensers 35 and 36, respectively. The potentiometer resistances 33 and 34 not only serve as potentiometer resistances, but also as protective resistances for the tube, so that the current through the tube cannot increase to a value which will destroy it. A feature of this circuit is the coupling between the tubes 25 and 26, this coupling comprising an output resistance 38 for tube 25, an input resistance 39 for tube 26, and a coupling condenser 40. A variable resistance 31 and bypass condenser 37 serve the same purpose in this circuit as corresponding elements 9 and 13 in Fig. 2.

Fig. 4 illustrates a transformer coupled plural stage amplifier the first tube 42 having an input circuit with a cathode return, while the second stage tube 43 has an input circuit with an anode return. This variation in connections has been found desirable for different tubes at different stages of amplification. This circuit employs tuned input circuits, the input circuit for tube 42 employing input transformer 45 and tuning condenser 46, while the input circuit for tube 43 comprises input transformer and tuning condenser 48. A variable resistance 41 and bypass condenser 44, and a similar resistance 54 and bypass condenser 67 polarize the control electrodes of tubes 42 and 43, respectively, to the proper value without decreasing the input voltages thereto. The power supply to the circuit is similar to that shown in Fig. 3 and consists of a power source 49, a potentiometer having sections and 51 and respective bypass condensers 52 and 53.

As better results have been obtained by the use of a pure resistance element as an output impedance instead of either an inductive or capacitive element, it has been found desirable in order to obtain an inductance coupling, to provide a resonant circuit which appears as a pure resistance to the tube. Such a coupling is shown in this circuit embodiment, the output circuit of tube 43 being tuned by a variable condenser 55 in shunt with the primary of output transformer 56. Further, the interstage coupling shown between tubes 42 and 43 in this circuit produces in the output circuit of tube 42 an effective resistance because of the resonant properties obtained by adjusting a condenser 48 with respect to the inductance in the transformer 4'7. It is to be understood, of course, that a condenser may be shunted across the primary of transformer 47 without departing from the spirit of the invention.

In the development of these cold electrode discharge tubes it has been found that power may be supplied to more than one tube from a potentiometer to which all of said tubes have a common connection. The schematic circuit in Fig. 5 illusstrates this type of system, tubes and 61 being supplied from a source 63 which may be either a direct current source or rectified alternating current. A potentiometer 64 is across the output of the source 63, a common connection being made to the negative terminal thereof. The anode of tube 60 is connected to the potentiometer 64 by a variable tap 66 while the anode of tube 61 is connected through adjustable tap 68. By-pass condensers '70 and '71 are connected across the respective portions of the potentiometer resistance 64 being used by the tubes. The tubes may be such that the subsequent stages take a lower voltage than the first stages. The remainder of the circuit is similar to that of Fig. 4 with the exception that tube 61 has the same type of return as that of 60. The polarizing resistances 5'7 and 59 with respective by-pass condensers 58 and are employed in the input circuits of tubes 60 and 61. The resistance of potentiometer 64 serves as a protective resistance but is so proportioned with respect to the tubes 60 and 61 that any variation in the operating characteristics of these tubes is negligible with respect to a similar variation in the resistance 64 so that both tubes always operate, the operation of one not affecting that of the other.

The above amplifying circuits employing three cold electrode tubes are described for the purpose of explaining the operation of these tubes, but other circuits will suggest themselves to those skilled in the amplifying art and it is to be understood that the above have been shown as typical examples of these circuits, the scope of the invention being defined by the appended claims.

What is claimed is:

1. In a plural stage amplifier, a plurality of glow discharge devices having cold electrodes, means for polarizing said electrodes to cause a glow to appear adjacent one of said electrodes in each tube, an inductive coupling between the output circuit of a preceding tube and the input circuit of a subsequent tube, and means for tuning the input circuit and output circuit of said tubes to obtain substantially a resistance impedance in the output circuits of said tubes.

2. In a plural stage amplifier, a plurality of glow discharge tubes having cold electrodes, an input circuit for one of said tubes connected between the cathode of said tube and a control electrode thereof, an input circuit for another of said tubes connected between the anode and control electrode thereof, and means for coupling the output circuit of said first tube with the input circuit of said second tube for amplifying currents transmitted therethrough.

3. In an amplifying system, a plurality of glow discharge tubes arranged for tandem amplification, an input circuit to the first of said tubes having inductance coupling, a resistance capacity coupling between respective tubes, a source of direct potential, a potentiometer connected across said source, and means for connecting the anode circuits of the respective tubes to mutually exclusive points of said potentiometer.

4. In a plural stage amplifier, a plurality of glow discharge tubes having all cold electrodes, means for connecting the first of said tubes to a source of potential to be amplified, means for connecting the last of said tubes to a utilization circuit, an inductance coupling between said glow discharge tubes, said inductance being tuned to appear as a substantially pure resistance to the output circuit of said first tube, a potentiometer, and means for connecting the anode circuits of said tubes to mutually exclusive points of said potentiometer.

AUGUST HUND. 

